The object of this project is to investigate the psychophysics of sensations arising from the teeth and to examine their physical and neurophysiological basis. Sensory modalities examined will be pain and mechanosensation. Stimuli will include thermal, electrical, chemical, osmotic, hydraulic (pressure), and mechanical displacement. Three types of experiments are planned. First, stimuli will be applied to teeth of human volunteers using specially constructed stimulation apparatus, and the subject will report the intensity and submodality ("quality") of the resulting sensation. Both predetermined stimulus patterns ("open loop") and stimulus modified online according to the subjects' response ("closed loop") will be employed. Data will be analyzed to determine what aspect of the stimulus is effective in evoking the sensation (strength, duration, rate of change, repetition rate) and whether particular stimuli evoke specific submodalities. Second, the role of intervening tissue in modifying the stimulus pattern actually reaching the afferent ending will be evaluated by means of models. Both mathematical models based upon computer simulation and physical models using extracted teeth will be employed. Third, the contribution to sensation of the sensory ending will be determined by recording from primary afferent neurons in experimental animals when stimuli are applied to the teeth. Comparison of the overall sensation with the properties of transmission through tissue and the characteristics of the afferent ending will permit evaluation of the contribution of the CNS to the elaboration of tooth sensation. Additional experiments are planned on the role of mechanosensation in bruxism and the nature of the "pre-pain" sensation.